Eyeglass rating with respect to protection against uv hazard

ABSTRACT

An index value is calculated for rating an eyeglass with respect to protection against UV hazard. The index value is based on an integrated UV transmission value through the eyeglass and an integrated UV reflection value related to a back face of the eyeglass. Thus, the index value takes into account actual wearing conditions where UV eye exposure is due either to transmission through the eyeglass or reflection on the eyeglass back face. Respective index values obtained for a set of eyeglasses allow easy sorting of the eyeglasses with respect to UV protection efficiency.

This document incorporates by reference application Ser. No. 14/003,159in its entirety.

The invention relates to a method of rating an eyeglass and also amethod of sorting a set of eyeglasses, with respect to protectionagainst UV hazard.

BACKGROUND OF THE INVENTION

Hazards due to UV radiation for human eyes have been suspected andstudied for long time. For example, document U.S. Pat. No. 5,949,535contains a presentation of some of the damages which may be caused by UVradiation upon the eye. In everyday life, most of the UV radiationencountered originates from the Sun, although some of the existingartificial light sources also produce significant amounts of UVradiation.

It is also known that eyewear can provide protection against UV hazardto a wearer. For example, the already-mentioned document U.S. Pat. No.5,949,535 discloses rating an eyewear according to its solar radiationprotection capabilities, in particular in the UV range. Then a user ofthe eyewear can be informed about its protection efficiency against UVhazard by providing him with a numeral value which quantifies thisprotection efficiency. The rating method disclosed in this prior artdocument is based on at least two of the following values: a firsttransmission value for each eyeglass in the UV wavelength range from 280nm (nanometer) to 400 nm, a second transmission value for each eyeglassin the blue wavelength range from 400 nm to 500 nm, and a further valuefor quantifying the amount of incident light that reaches the eye fromaround the frame which holds the eyeglass on the wearer's face. Moreprecisely, this latter value represents the extraneous light thatreaches the eye without being filtered through the eyeglass or absorbedor reflected by the eyewear frame.

But this known rating method does not quantify appropriately in allcircumstances the total UV radiation amount which enters into the eye ofthe eyewear wearer. In particular, there exists some conditions wheresignificant amount of radiation enters into the eye but without beingtaken into account by this method.

Therefore, an object of the present invention is to provide rating of aneyeglass that quantifies more significantly the protection against UVhazard which is produced by the eyeglass. In particular, the ratingshould take into account most of the actual conditions of UV eyeexposure which occur actually.

Another object of the present invention is to provide a value for ratingan eyeglass with respect to UV protection, which can be understoodeasily and directly by a customer intending to acquire the eyeglass.

Still another object of the invention is to provide a rating value foran eyeglass with respect to UV protection, which can be determinedeasily, in particular by measuring and/or calculating appropriateoptical values.

SUMMARY OF THE INVENTION

For meeting these objects and others, a first aspect of the inventionproposes a method of rating an eyeglass with respect to protection whichis provided by this eyeglass against UV hazard, whereby an index valueis calculated for quantifying a reduction in a total UV amount thatimpinges onto an eye for a wearer of the eyeglass with respect to UVexposure without eyeglass, the method comprising the following steps:

-   -   /1/ providing a value of UV transmission for the eyeglass,        obtained by integrating spectral transmission values weighted        for quantifying hazard and intensity for each wavelength value,        over a determined UV wavelength range;    -   /2/ providing a value of UV reflection on a back face of the        eyeglass, the

UV reflection being obtained by integrating spectral reflection valuesrelating to the back face of the eyeglass, and weighted for quantifyingthe hazard and intensity for each wavelength value, over the determinedUV wavelength range;

-   -   /3/ combining both values of UV transmission and UV reflection        of the eyeglass using an addition formula with non-zero positive        factors respectively for the UV transmission and UV reflection;        and    -   /4/ calculating the index value from a base number divided by a        result obtained in step /3/.

Thus, the rating method of the invention is efficient for taking intoaccount varying eye exposure conditions to UV radiation. First ones ofthese conditions occur when the wearer's face is oriented towards the UVsource. Then, the transmission of UV radiation through the eyeglass isthe main exposure mode of the wearer's eye to UV radiation, and thiscontribution participates to the index value through the UV transmissionvalue of the eyeglass involved in the addition formula.

But second exposure conditions also occur when the wearer's face isoriented away from the UV source, for example with an angle of between135° and 160° between the direction of the UV source and the forwarddirection of the wearer's face. In such conditions, no UV radiation istransmitted through the eyeglass to the eye, but some radiation impingesonto the back face of the eyeglass from the UV source around thewearer's head, mainly on both external lateral sides, and is reflectedby the eyeglass to the eye. This other exposure mode is separate fromthat which involves transmission through the eyeglass, but alsoparticipates to the UV eye exposure when the wearer is equipped with theeyeglass. According to the invention, this reflection-based exposuremode also participates to the index value, through the UV reflectionvalue which is also involved in the addition formula.

Hence, the rating method of the invention is efficient for taking intoaccount UV eye exposure conditions due to radiation transmission throughthe eyeglass but also radiation reflection by the back face of theeyeglass.

Optionally, the index value may be obtained in step /4/ from the ratioof the base number to the result for the addition formula filled in withthe UV transmission and UV reflection values of the eyeglass, by furtherimplementing an offset or correcting term. Such offset or correctingterm may be added to the ratio of the base number to the result of theaddition formula. It may depend on geometric parameters such as positionof the UV source with respect to the eyeglass, spectacle frameparameters, physionomic parameters of the wearer, lens sizing andcurvature parameters, etc.

Preferably, the index value calculated in step /4/ may be equal to thebase number divided by the result obtained in step /3/ for the combiningof the UV transmission and UV reflection values of the eyeglass usingthe addition formula.

In preferred implementations of the invention, the result of theaddition formula may be unity when replacing in this formula the UVtransmission of the eyeglass with a maximum value due to a scale usedfor the UV transmission, and also replacing the UV reflection of theeyeglass with zero. Then, the result of the addition formula when usingthe UV transmission and the UV reflection values of the eyeglass mayequal a reduction factor for the total UV eye exposure when the weareris equipped with the eyeglass, as compared with the wearer withouteyeglass. Put another way, the result of the addition formula quantifiesthe efficiency of the eyeglass for protecting the eye against UV hazardin everyday life. Such meaning of the index value provided by theinvention is easy and simple to understand.

The invention may be used for rating an eyeglass with respect to hazardrelated to any UV source, natural or artificial, provided that theweighting function used in steps /1/ and /2/ corresponds to this UVsource. This comprises that the weighting function for the spectraltransmission and reflection values of the eyeglass is based on spectralirradiance values which correspond to the actual UV source. When the Sunis the UV source considered, the quantifying of intensity for eachwavelength value in steps /1/and /2/ may be implemented by using valuesof solar spectral irradiance as a factor within a weighting function forthe spectral transmission and spectral reflection values of theeyeglass.

Preferably, the addition formula used in step /3/ may beα·R_(UV)+β·τ_(UV)+γ, where τ_(UV) and R_(UV) are respectively the UVtransmission and the UV reflection of the eyeglass, α and β are thefactors respectively for the UV reflection and the UV transmission ofthe eyeglass, and γ is a constant value. The constant value γ may benon-zero. Then, it may stand for a UV intensity amount which includessolar UV radiation diffused before entering into a wearer's eye. This UVintensity amount may also include direct solar UV radiation withincidence direction such that this radiation enters into the wearer'seye after passing outside a peripheral edge of a frame used with theeyeglass when the wearer is equipped with the eyeglass. In both cases,the constant value γ may be obtained from measurements performed withreference conditions in day time, of the UV intensity amount includingthe solar UV radiation diffused before entering into the wearer's eye,and possibly also including the direct solar UV radiation which entersinto the wearer's eye from around the eyeglass.

In alternative preferred implementations of the invention, the factorsfor the UV reflection and the UV transmission values of the eyeglass inthe addition formula may be both equal to unity, and the constant valuemay be zero. Very simple calculations then lead to the index value forany eyeglass.

The determined UV wavelength range which is used in both steps /1/ and/2/ may be either a first range from 280 nm to 380 nm, or a second rangefrom 280 nm to 400 nm, or a third range from 315 nm to 380 nm, or afourth range from 280 nm to 315 nm.

A second aspect of the invention proposes a method of sorting a set ofeyeglasses with respect to protection provided by each of theseeyeglasses against UV hazard, which method comprises the followingsteps:

-   -   for each one of the eyeglasses, calculating a respective index        value by implementing a rating method as described above; and    -   comparing with each other the index values obtained respectively        for the eyeglasses.

Thus, a customer who intends to acquire one of the eyeglasses can selectit based on clear information about their respective protectionefficiencies against UV hazard. He can sort the eyeglasses with respectto their index values while being aware of an absolute protectionefficiency of each eyeglass compared to bare-eye conditions.

The invention is described now in detail for non-limitingimplementations, with reference to the figures now listed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates radiation streams impinging onto an eye of aneyeglass wearer.

FIGS. 2 a and 2 b reproduce mathematical expressions for calculating UVtransmission and UV reflection values for an eyeglass.

FIG. 2 c is a table containing spectral weighting values which may beused in implementations of the invention.

FIGS. 3 a and 3 b reproduce possible mathematical expressions suitablefor calculating an index value according to the invention.

For sake of clarity, the elements represented in FIG. 1 are not sized inrelation with actual dimensions, nor with ratios of actual dimensions.In addition, same characters used in different figures have identicalmeaning.

DETAILED DESCRIPTION OF THE INVENTION

The UV part of the solar radiation which is transmitted through theEarth atmosphere is usually divided into two wavelength ranges: UV Acorresponding to wavelength values from 380 nm (nanometer) at theboundary with the visible range down to 315 nm, and UV B for wavelengthvalues from 315 nm down to 280 nm. UV radiation originating from the Sunwith wavelength below 280 nm, denoted UV C, is absorbed by the ozone ofthe atmosphere, so that anyone is not exposed to UV C in everyday life,unless exceptional conditions which are not encountered by most ofpeople. In addition, radiation with wavelength comprised between 380 nmand 400 nm may also be considered as pertaining to the UV range.However, in the detailed description below and unless indicateddifferently, the UV wavelength range considered for solar radiation mayextend from 280 nm to 380 nm, although the invention may be applied toother UV ranges.

In a known manner, UV A radiation is absorbed by the eye crystallinelens of a human being, and the most important part of the UV B radiationis absorbed by the cornea. Known ocular pathologies are related to theseUV radiations, so that protection of the eye against UV exposure is anissue with growing interest. In particular, UV B radiation is known tobe more dangerous than UV A radiation. The present invention aims atquantifying such protection for eyeglasses such as spectacle eyeglasses,in a simple to calculate and understand but meaningful way.

It applies to any spectacle eyeglass: ametropia-correcting eyeglass,progressive addition eyeglass, multifocal eyeglass, plano eyeglass,solar glass, etc, whatever the base material of the eyeglass: mineral,organic or hybrid. It also applies to eyeglasses which are provided withone or more coatings or layers on at least one of their optical faces,namely their front face, back face, both front and back faces, and/orpossibly on an additional interface of the eyeglass located between thefront face and the back face. In particular, it applies to eyeglasseswhich are provided with anti-reflecting coatings on their back face, asit will be indicated later on that such reflection is important in somecircumstances.

The invention also applies to eyeglasses for goggles, whatever is thecurvature of the eyeglass, the exact form of the frame, in particularthe lateral parts of the frame, the material of the frame, etc. Inparticular, the invention is compatible with configurations where asingle elongated eyeglass extends continuously in front both eyes of thewearer. It is also compatible with lateral parts of the frame which areUV transmitting or UV blocking.

FIG. 1 shows schematically several radiation flows which impinge ontothe eye of the eyeglass wearer. Reference numbers 1, 1 a and 1 b denoterespectively the eyeglass, its front face and its back face. Theradiation flows are now listed:

-   -   T: the radiation originating directly from the Sun and        transmitted through the eyeglass 1, from the front face 1 a to        the back face 1 b, and then reaching the eye;    -   R: the radiation originating directly from the Sun and reflected        on the back face 1 b of the eyeglass 1, and then reaching the        eye;    -   D₁: the radiation originating directly from the Sun, passing        around the eyeglass 1 outside the peripheral edge of this latter        and a frame used with the eyeglass 1, and reaching the eye;

D₂: the radiation originating indirectly from the Sun, because of beingdiffused by elements contained in the wearer's environment such asground or water surface before passing around the eyeglass 1 andreaching the eye; and

D₃: the radiation originating indirectly from the Sun, because of beingdiffused by the wearer's skin or the eyeglass frame before reaching theeye.

These radiation flows apply in particular for UV radiation.

The radiation flows T and R depend on the eyeglass features, inparticular on its values of transmission and reflection respectively.But they may also depend on further eyeglass features such as theeyeglass dimensions, the base value, the prism value, the pantoscopicangle value, etc. As well-known in ophthalmics, the base value of aneyeglass relates to its curvature value at a reference point in itsfront face. Because of the originating directions of the radiation flowsT and R with respect to the eyeglass 1, these flows T and R do not existsimultaneously. Indeed, the radiation flow T is non-zero when thewearer's face is oriented towards Sun side, and then direct solarradiation cannot reach the back face 1 b of the eyeglass 1. Conversely,the radiation flow R is non-zero when the wearer's face is oriented awayfrom Sun side, and then direct solar radiation cannot reach the frontface 1 a of the eyeglass 1 for passing through this latter. Butradiation flows T and R may occur after one another when the eyeglasswearer is turning from facing initially South direction until facingNorth side with about 30° offset from the North direction.

In addition, the radiation flow T impinges on the front face 1 a of theeyeglass 1 with a value for the incidence angle i_(T) which depends onthe azimuth-orientation of the wearer's head, but also the time withinthe day period and the latitude at the surface of the Earth for the Sunheight, the pantoscopic angle, etc. However, because transmissionusually changes only with limited extent as long as the incidence anglei_(T) is not too large, one may consider that the value for thetransmission through the eyeglass 1 at 0° (degree) for the incidenceangle i_(T) nearly always applies. The incidence angle is measured withrespect a reference direction FD which oriented forwards for theeyeglass 1, i.e. ahead from the front face 1 a.

The value of the incidence angle i_(R) for the radiation flow R on theeyeglass back face 1 b needs to allow for the flow R to propagatebetween the edge of the eyeglass 1 and the wearer's head. Because ofthat, the value of the incidence angle i_(R) of the radiation flow R,again with respect to the reference direction FD, is between 135° and160°, more often between 145° and 150°. Such angle values do not appearactually in FIG. 1, because the propagation direction of the radiationflow R is not contained within the sectional plane of this figure. It isrepeated again that direct solar radiation is not transmitted throughthe eyeglass 1 with i_(T)-angle and reflected with i_(R)-angle at thesame time.

Radiation flows D₁ to D₃ do not depend of the eyeglass transmission andreflection values, but they may depend on other parameters such as theeyeglass dimensions, geometrical features of the frame and the wearer'sface, etc. In addition, energy spectral distributions of the radiationflows D₂ and D₃ do not depend only on the solar irradiance, becausethese flows are diffused before reaching the eye. For this reason, thespectral diffusion efficiency of the diffusing elements may play asignificant role. By way of simplicity, the respective radiationenergies of the flows D₁ to D₃ at the eye surface may be summed within aresulting radiation contribution D, so that D=D₁+₂+D₃. For somecircumstances where the total energy value of the radiation contributionD is much less than the energy amount of the radiation flow T or R, orfor sake of simplicity in the index value calculation, one may considerthat radiation contribution D equals zero.

International Standard ISO 13666 indicates a manner for calculating atransmission in the solar UV A spectrum, as well as a transmission inthe solar UV B spectrum. Both are expressed as continuous sums, i.e.integration, over the corresponding UV A and UV B wavelength ranges, ofthe spectral transmission of the eyeglass weighted with the solarspectral irradiance Es(λ) multiplied by a relative spectraleffectiveness function S(λ) for UV radiation. The product of Es(λ) withS(λ) then appears as the actual weighting function of the spectraltransmission, and is denoted W(λ). In the context of the presentdescription, transmission and transmittance are used equivalently,provided that the Man skilled in optics knows that they areinter-related by a reference area factor.

FIG. 2 a contains an expression for the transmission of the eyeglass inthe UV total solar spectrum, corresponding to UV A and UV B spectrajoined together. This expression is consistent with those of theStandard ISO 13666 for the UV A and UV B ranges separately. Inaccordance with the indications reported above, the total solar spectrumUV A & UV B may correspond to the wavelength range extending from 280 nmto 380 nm. τ(λ) denotes the spectral transmission through the eyeglass,and τ_(UV) is the UV transmission of the eyeglass, also called mean UVsolar transmission of the eyeglass.

FIG. 2 b corresponds to FIG. 2 a for the UV radiation reflection on theback face of the eyeglass. R(λ) denotes the spectral reflection on theeyeglass back face, and R_(UV) is the UV reflection on the eyeglass backface, also called mean UV solar reflection of the eyeglass.

In both expressions of the UV transmission and UV reflection of FIGS. 2a and 2 b, the continuous sums over the UV wavelength range may bereplaced with discrete sums, for example using a wavelength pitch of 5nm. Other wavelength pitch values may be used alternatively, providedthat the values of the solar spectral irradiance Es(λ) and the relativespectral effectiveness function S(λ) are interpolated appropriately.Annex A of Standard ISO 13666 contains a table which is reproduced inFIG. 2 c, with the values of the solar spectral irradiance Es(λ) and therelative spectral effectiveness function S(λ) for each UV wavelength Awith a 5 nm pitch, from 280 nm to 380 nm. This table can thus be usedfor calculating the UV transmission and UV reflection values.

FIG. 3 a displays a possible mathematical formula for the index value ofthe invention. This index is denoted E-SPF® standing for eye-solarprotection factor. In this formula:

-   -   BN is a base number which is constant and non-zero, and acts as        a scale factor for the index;    -   τ_(UV)(i^(R)) is the UV transmission of the eyeglass as        described above, assessed for the incidence angle value i_(R);    -   R_(UV)(i_(R)) is the UV reflection of the eyeglass back face as        described above, assessed for the incidence angle value i_(R);    -   α and β are the factors respectively of the UV reflection R_(UV)        and the UV transmission τ_(UV); and    -   γ is a constant value.

For consistency with the geometrical considerations reported withreference to FIG. 1, the UV transmission τ_(UV) may be provided for afirst value of the incidence angle i_(T) of UV rays onto the eyeglass 1,which is less than 30°. The UV reflection R_(UV) may be provided for asecond value of the incidence angle i_(R) of the UV rays onto the backface 1 b of the eyeglass 1, which is between 135° and 160°, with bothincidence angles I_(T) and i_(R) measured from the forward-orientedreference direction FD of the eyeglass.

Using non-zero values for both factors α and β enables that the indexvalue obtained is meaningful for conditions where the UV eye exposure isdue to radiation transmission through the eyeglass, but also when the UVeye exposure is due to radiation reflection on the back face of theeyeglass. This is especially advantageous since UV eye exposure byback-face reflection may form the most important contribution to thetotal exposure over a long time-period in some cases, for example withsunglasses with large open gaps between the lateral eyeglass edges andthe wearer's temples, and for conditions where the solar height is low.

Preferably, the ratio of the factor β to the base number BN, i.e. β/BN,may be in the range from 0.01 to 1. Similarly, the ratio α/BN may alsobe in the same range from 0.01 to 1. More preferably, α/BN is equal toor higher than, 0.2, 0.4, 0.5 or 0.6 in the order of increasingpreference, while remaining less than or equal to 1. In parallel, β/BNis equal to or higher than, 0.4, 0.5, 0.6 or 0.7 also in the order ofincreasing preference, again while remaining less than or equal to 1. Apreferred combination is α/BN and β/BN both in the range from 0.5 to 1.

Generally, factors α and β stands in particular for the role ofgeometrical factors relating to the eyeglass or eyeglass wearingconditions, such as the eyeglass area for factor β, and the area of theopen gap between the eyeglass and the wearer's temple for factor α. Bothfactors β and α may be obtained from photometric measurements performedrespectively for direct solar UV intensity impinging onto a wearer's eyeand direct solar UV intensity impinging onto the back face of theeyeglass from back side of the wearer's head, respectively correspondingto the radiation flows T and R. For such measurements, reference valuesmay be used for parameters which are selected among illuminationparameters in day time, sizing and wearing parameters of a spectacleframe used with the eyeglass, and the base parameter of the eyeglass. Insome implementations of such measurements, the factors α and β may beobtained from averaged measurement results which are performed withvarying some of the illumination parameters selected among solar time,azimuth direction of the wearer's head, inclination of the wearer'shead, season, date within the year, latitude on the Earth, etc.

The constant value γ stands for the total radiation contribution D. Itmay be zero for simplified implementations of the invention, or may benon-zero with value obtained from measurements performed with referenceconditions in day time, of a UV intensity amount including the solar UVradiation flows D₂ and D₃ which are diffused before reaching thewearer's eye. In this case, the UV intensity amount which is measuredfor obtaining the constant value γ, may further include the direct solarUV radiation flow D1 with incidence direction such that this radiationflow reaches the wearer's eye after passing outside the peripheral edgeof the frame used with the eyeglass when the wearer is equipped so.

The factors α and β and the constant value γ may be determined byirradiance measurements using a sensor placed at the eye location on thehead of a dummy model simulating the wearer. The measurements areconducted in a solar environment, while the eyeglass is mounted inspectacles on the model's head in the same position as if it were wornactually by the wearer.

In a first experiment, the back face of the eyeglass is covered by aUV-blocking material, for example an opaque material absorbing allvisible and UV rays impinging onto the front face of the eyeglass andtransmitted to its back face, as well as UV rays impinging onto the backface. Thus no UV ray reaches the sensor, which would originate fromforwards through the eyeglass and from backwards with reflection ontothe eyeglass back face. The γ constant value can then be determined.

In a second experiment, the UV-blocking material is covered onto thefront face of the eyeglass. The sensor measures then, in addition to γconstant value, the irradiance part due to the reflection on the backface of the eyeglass. The value of the factor α can thus be calculated.

In a third and last experiment, the whole irradiance received by the eyeof the wearer is measured by the sensor, and the value of the factor βcan also be obtained.

FIG. 3 b corresponds to FIG. 3 a for a preferred implementation of theinvention. In this implementation, the factors α and β of both the UVreflection R_(UV) and the UV transmission τ_(UV) are equal to unity, andthe constant value is zero: α=β=1 and γ=0. The base number BN may beequal to unity too. For example, the E-SPF value thus calculated may bebased on a value for the UV reflection which is assessed for theincidence angle i_(R) of 145°, and a value for the UV transmission whichis assessed for the incidence angle i_(T) of 0°. Such E-SPF value iseasy to calculate for any eyeglass, from UV transmission and UVreflection values obtained in accordance with the formulae of FIGS. 2 aand 2 b.

The expression of FIG. 3 b for the E-SPF index has been used for ratingfour eyeglasses obtained by combining two base eyeglasses with twoanti-reflecting coatings arranged on the back faces of the baseeyeglasses. The first base eyeglass, denoted base eyeglass 1, has a UVtransmission τ_(UV)(0°) at zero value for the incidence angle i_(T)which is equal to about 5%, and the UV transmission τ_(UV)(0°) of thesecond base eyeglass, denoted base eyeglass 2, is zero. The firstcoating, denoted coating 1, is efficient mainly in the visiblewavelength range, whereas the second coating, denoted coating 2, hasbeen optimized for minimizing back face reflection in the UV range atabout 145° for the incidence angle i_(R). Thus, for both base eyeglasses1 and 2, the UV reflection R_(UV)(145°) of coating 1 equals around 13%,and that of coating 2 equals around 4%. The table here-below gathers theE-SPF values which are obtained for the four eyeglasses:

Base eyeglass 1 Base eyeglass 2 τ_(UV)(0°) = 5% τ_(UV)(0°) = 0% Coating1 Eyeglass 1 Eyeglass 2 R_(UV)(0°) = 13% E-SPF = 6 E-SPF = 8 Coating 2Eyeglass 3 Eyeglass 4 R_(UV)(0°) = 4% E-SPF = 11 E-SPF = 25

Thus, the invention enables to sort easily and efficiently theeyeglasses with respect to the eye protection which is provided by eachof them against UV hazard. First, the respective index value iscalculated for each one of the eyeglasses. Then, the index values whichhave been obtained respectively for the eyeglasses are compared witheach other.

Generally for the present invention, the result of the addition formulaat the denominator of the index value, namely α·R_(UV)+β·τ_(UV)+γ, maybe obtained directly from measurements performed with the eyeglass usinga bench photometer designed for simulating outside illuminationconditions in day time. To this purpose, UV sources possibly withfilters selected so as to reproduce the weight function W(λ) may belocated in front of the eyeglass 1, and behind it with angular offsetequal to 180°-i_(R), and optionally additional UV sources forreproducing the radiation flows D₁ to D₃. All UV sources are activatedsimultaneously, and a UV photometer located behind the eyeglass capturesthe total UV radiation amount at the location of the wearer's eye withrespect to the eyeglass.

The invention may be implemented while adapting or modifying somedetails with respect to the specification just above, but maintaining atleast some of its advantages. In particular, the numeral values citedare only for illustrative purpose, and may be adapted.

Additionally, alternative implementations of the invention may beobtained by modifying the wavelength range of the UV radiations, whichis used for calculating both values of the UV transmission τ_(UV) andthe UV reflection R_(UV). Then, the index value E-SPF is obtained forthe UV wavelength range selected, based on the values of the UVtransmission τ_(UV) and UV reflection R_(UV) which have been calculatedfor this selected UV wavelength range. The modified UV wavelength rangeis thus to be taken into account in the formulae of FIGS. 2 a and 2 b inplace of UVA & UVB ranging as a whole from 280 nm to 380 nm, and theresulting modified results for the UV transmission τ_(UV) and UVreflection R_(UV) will propagate into the formulae of FIGS. 3 a and 3 b.

In first ones of these alternative implementations, the UV wavelengthrange from 280 nm to 380 nm as used before in the detailed descriptionmay be replaced with the extended UV wavelength range from 280 nm to 400nm.

In second ones of the alternative implementations, the UV wavelengthrange may be limited to the UV A radiations, from 315 nm to 380 nm.Then, the formulae of FIGS. 2 a and 2 b lead to values for a UV Atransmission value, namely τ_(UV A), and a UV A reflection value,R_(UV A). A value for the index E-SPF is then obtained which relates tothe UV A radiations only: E-SPF(UV A).

Third alternative implementations are obtained in a similar manner byusing the UV B wavelength range only: from 280 nm to 315 nm, instead ofthe UV A wavelength range of the second implementations. Thus, a UV Btransmission value τ_(UV B), a UV B reflection value R_(UV B) and avalue for the index E-SPF(UV B) are obtained, which relate to the UV Bradiations.

However, one should pay attention about the following inequalities:

-   -   τ_(UV A)+τ_(UV B)≠τ_(UV) as this latter τ_(UV) is shown in FIG.        2 a using the merging of the UV A and UV B ranges,    -   R_(UV A)+R_(UV B)≠R_(UV) as the latter R_(UV) is shown in FIG. 2        b using the merging of the UV A and UV B ranges, and

E-SPF(UV A)+E-SPF(UV B)≠E-SPF as this latter E-SPF value results fromthe formula of FIG. 3 a or 3 b where the values of τ_(UV) and R_(UV) areobtained for the merging of the UV A and UV B ranges.

1-16. (canceled)
 17. A method of rating an eyeglass with respect toprotection provided by the eyeglass against UV hazard, whereby an indexvalue is calculated for quantifying a reduction in a total UV amountimpinging onto an eye for a wearer of the eyeglass with respect to UVexposure without eyeglass, the method comprising: a) providing a valueof UV transmission for the eyeglass, obtained by integrating spectraltransmission values weighted for quantifying hazard and intensity foreach wavelength value, over a determined UV wavelength range; b)providing a value of UV reflection on a back face of the eyeglass, theUV reflection being obtained by integrating spectral reflection valuesrelating to the back face of the eyeglass, and weighted for quantifyingthe hazard and intensity for each wavelength value, over the determinedUV wavelength range; c) combining both values of UV transmission and UVreflection of the eyeglass using an addition formula with non-zeropositive factors respectively for the UV transmission and UV reflection;and d) calculating the index value from a non-zero base number dividedby a result obtained in the combining c).
 18. A method according toclaim 17, wherein the index value calculated in the calculating d) isequal to the base number divided by the result obtained in the combiningc) for the combining of the UV transmission and UV reflection values ofthe eyeglass using the addition formula.
 19. A method according to claim17, wherein the result of the addition formula is unity when replacingin the addition formula the UV transmission of the eyeglass with amaximum value due to a scale used for the UV transmission, and alsoreplacing the UV reflection of the eyeglass with zero, and wherein theresult of the addition formula when using the UV transmission and the UVreflection values of the eyeglass equals a reduction factor for thetotal UV eye exposure when the wearer is equipped with the eyeglass, ascompared with the wearer without eyeglass.
 20. A method according toclaim 17, wherein the quantifying of intensity for each wavelength valuein the providing a) and providing b) includes using values of solarspectral irradiance as a factor within a weighting function for thespectral transmission and spectral reflection values of the eyeglass.21. A method according to claim 17, wherein the UV transmission isprovided in the providing a) for a first value of an incidence angle ofUV rays onto the eyeglass less than 30°, and the UV reflection isprovided in the providing b) for a second value of incidence angle of UVrays onto the back face of the eyeglass between 135° and 160°, theincidence angles being measured from a forward-oriented referencedirection of the eyeglass.
 22. A method according to claim 17, wherein aratio of the factor for the UV transmission of the eyeglass used in thecombining c) to the base number is in a range of from 0.01 to
 1. 23. Amethod according to claim 17, wherein a ratio of the factor for the UVreflection on the back face of the eyeglass used in the combining c) tothe base number is in a range of from 0.01 to
 1. 24. A method accordingto claim 17, wherein the factors for the UV transmission and the UVreflection used in the combining c) for the eyeglass are obtained fromphotometric measurements performed respectively for direct solar UVintensity impinging onto the wearer's eye and direct solar UV intensityimpinging onto the back face of the eyeglass from back side of awearer's head, with reference values for parameters selected in a listcomprising illumination parameters in day time, sizing and wearingparameters of a spectacle frame used with the eyeglass, and a baseparameter of the eyeglass.
 25. A method according to claim 24, whereinthe factors for the UV transmission and the UV reflection used in thecombining c) for the eyeglass are obtained from averaged measurementresults performed with varying some of the illumination parametersselected among solar time, azimuth direction of the wearer's head,inclination of the wearer's head, season, date within year, and latitudeon the Earth.
 26. A method according to claim 17, wherein the additionformula used in the combining c) is α·R_(UV)+β·τ_(UV)+γ, wherein: τ_(UV)and R_(UV) are respectively the UV transmission and the UV reflection ofthe eyeglass, α and β are the factors respectively for the UV reflectionand the UV transmission of the eyeglass, and γ is a constant value. 27.A method according to claim 26, wherein the factors of the UV reflectionand the UV transmission values of the eyeglass in the addition formulaare both equal to unity, and the constant value is zero.
 28. A methodaccording to claim 26, wherein the constant value is nonzero and isobtained from measurements performed with reference conditions in daytime, of a UV intensity amount including solar UV radiation diffusedbefore entering into a wearer's eye.
 29. A method according to claim 28,wherein the UV intensity amount measured for obtaining the constantvalue further includes direct solar UV radiation with incidencedirection such that the direct solar UV radiation enters into thewearer's eye after passing outside a peripheral edge of a frame usedwith the eyeglass when the wearer is equipped with the eyeglass.
 30. Amethod according to claim 17, wherein the result of the addition formulais obtained directly from measurements performed with the eyeglass usinga bench photometer configured to simulate outside illuminationconditions in day time.
 31. A method according to claim 17, wherein thedetermined UV wavelength range used in the providing a) and theproviding b) is selected in the list comprising a first range from 280nm to 380 nm, a second range from 280 nm to 400 nm, a third range from315 nm to 380 nm, and a fourth range from 280 nm to 315 nm.
 32. A methodof sorting a set of eyeglasses with respect to protection provided byeach of the eyeglasses against UV hazard, comprising: for each one ofthe eyeglasses, calculating a respective index value by implementing arating method according to claim 17; and comparing with each other theindex values obtained respectively for the eyeglasses.